BTW: I think that this the sort of service where Freemium doesn't make sense. You need people to get value out of the system, not offer them some crippled version for free and hope they will upgrade.
With this sort of service it is best to offer everything with a generous trial period.
Once someone has their data in your system they will want to pay you when the time comes as they have invested their time to get their data into your system. But getting people to convert will depend on whether you are offering them true value, and this can be best achieved by exposing all the value from the start.